Hydrostatic quirk or total nonsense?

[civilian]

OP, when trying to lift things out of the semi trailer, try this after observing other safety measues. When I want to lift a heavy bunk of freshly sawn 12 ft lumber on my B26TLB, I enter the stack until the back of the forks hit the stack. Fork frame straight up/down. Then raise the fork back up while tipping the tips down. Continue until FEL won't lift an more, then curl back and continue your lift.

I had to do this yesterday stacking a second bunk on the first. Couln't raise forks high enough to get on fully on bottom bunk. But the tips were high enough to set the tips on the bottom bunk. Uncurling while raising the forks allowed me lift lift high enough and then curl back to set the second bunk on top of the bottom one. Jon

 

[npalen]

OP, when trying to lift things out of the semi trailer, try this after observing other safety measues. When I want to lift a heavy bunk of freshly sawn 12 ft lumber on my B26TLB, I enter the stack until the back of the forks hit the stack. Fork frame straight up/down. Then raise the fork back up while tipping the tips down. Continue until FEL won't lift an more, then curl back and continue your lift.

I had to do this yesterday stacking a second bunk on the first. Couln't raise forks high enough to get on fully on bottom bunk. But the tips were high enough to set the tips on the bottom bunk. Uncurling while raising the forks allowed me lift lift high enough and then curl back to set the second bunk on top of the bottom one. Jon

I'm sure most of us have used tactics like this to get "just a little bit more lift". Just be aware that it puts more weight on the loader than the relief valve normally would as the relief is isolated from the lift circuit when using the curl.

 

[civilian]

When the loader will lift up but not high enough to load on the deckover trailer, I have also driven up a set of 2x material car ramps. Jon

 

[Bentrim]

Hydraulics a very simple and confusing topic.
Open Center system. Pump = A positive displacement unit that draws oil from a tank and moves oil to a control device, note a pump does not create pressure it only moves fluid at a set rate per the rpm operated. Control Valve = a device that receives oil form a pump and if not directing oil to a cylinder or motor returns it to the tank. If directing oil it directs the oil to the cylinder or motor. Note most contain a relief valve. To this point system has only pressure high enough to move the oil thru the system. Once the valve directs the oil to cylinder the cylinder will move, pressure in the system will increase until it moves the load. If the load is too much, movement will stop, pressure will increase until the relief valve opens. Note if engine speed is increased so will the GPM. Force may be increased due to the volume of oil not able to flow thru the relief valve, or a volume increase due to a worn pump or other leakage in the valve or cylinder. The speed of cylinder movement is directly affected by pump rpm. This type system can use many valves in series as long as a power beyond fitting is used. For operation of a constant flow this system requires lowest pressure and maximum gpm used or you will overheat it.
Closed center system uses a variable displacement pump and a closed center valve otherwise is the same for cylinders and motors as above. When this pump reaches system pressure it shuts down to almost no flow. Pressure is the same with engine idling or wide open but gpm will increase with speed. It needs minimal flow in the system for lubrication, cooling, and leakage. To best describe a closed center system think of the water system in your house. Multiple valves can be used in the system by just adding a T in the main pressure line. for continuous use you must use minimum flow or the system will overheat. These systems usually do not need relief valves due to the pump controls the highest pressure. These pumps can be gravity or pressure fed. Manufactures use then because when the system is not being used it frees up engine power but is more costly than an open center systems,
Hydrostatic A bidirectional variable displacement pump connected by a closed loop to a motor. Usually kept charged by an open center charge pump, this pump can also operate as an implement lift. The charge circuit is set to a specified pressure. The main circuit has relief valves and may contain acceleration control valves. Speed of the motor is affected by engine speed and controlling the displacement of the pump. Also direction of the motor is controlled by the movement of the swashplate in the pump. Most garden tractors and zero turns do not use a transmission, most scuts, cuts, farm tractors, or industrial equipment use a multiple speed transmission, for low speed control high torque or high speed low torque.

 

[sunandsand]

I hadn't considered the extra weight of the quick disconnect - and it isn't light.


Interesting that tilt function doesn't (seem to) be connected with the safety valve (if I read it correctly), which is why I couldn't lift, but I could still tilt. That got me just enough extra height to get the pallets out of the truck.


In the meantime, I have solved this problem by advising the shipper that he better not send me any more rocks. If he does, I am going to hire some people to unload the top half of each pallet manually, and he is going to have to pay a LOT for this. He's no dummy, we've been doing business for over 20 years, and he listens to me.


Safety procedures - wear ear protectors and control the work zone. Chase away spectators, lookie-loos, cheerleaders, photographers, basically everyone who isn't directly involved with the unloading. Everybody STANDS STILL and does not move without my explicit instructions. Stand here, back up 15 feet, guide me into the hangar, etc.

Since the truck doesn't move during unloading, lift the pallets just enough to clear the lip at the back of the truck, back away SLOWLY and in a straight line, then lower the pallet down to ground level as soon as it clears the back of the truck. When moving the pallet into the hangar, the pallet will be no more than 6" off the ground.

I do need to be guided since I can't see through the boxes on the pallet. I have to turn 90 degrees and go up a small slope to the entry to the hangar, I drive slowly and cross all slopes at a 90 degree angle, don't let the tractor or the load tilt.

I use the phrases "Moving forward", "Moving back" and "Are you clear?" a lot, and listen for positive confirmation before moving the tractor. I have noticed that people tend to move in for a closer look as work progresses, so I am not shy about chasing them away again to a safe vantage point.

As I mentioned, I have had people walk between the tractor (while it is running) and the truck, and I have had people get within five feet of the tractor when I am making turns (usually standing on the outside of the turn, which is where the boxes will fall if anything goes wrong). I've found that I cannot assume anyone else understands the dangers here, so it is my job to keep them safe, and if they get insulted, that's just too g*****n bad, I'd rather they get insulted than hurt or worse.

People do dumb things all the time, I really, really prefer they do them someplace else.

Best Regards,

Mike/Florida

 

[npalen]

I hadn't considered the extra weight of the quick disconnect - and it isn't light.


Interesting that tilt function doesn't (seem to) be connected with the safety valve (if I read it correctly), which is why I couldn't lift, but I could still tilt. That got me just enough extra height to get the pallets out of the truck.


In the meantime, I have solved this problem by advising the shipper that he better not send me any more rocks. If he does, I am going to hire some people to unload the top half of each pallet manually, and he is going to have to pay a LOT for this. He's no dummy, we've been doing business for over 20 years, and he listens to me.


Safety procedures - wear ear protectors and control the work zone. Chase away spectators, lookie-loos, cheerleaders, photographers, basically everyone who isn't directly involved with the unloading. Everybody STANDS STILL and does not move without my explicit instructions. Stand here, back up 15 feet, guide me into the hangar, etc.

Since the truck doesn't move during unloading, lift the pallets just enough to clear the lip at the back of the truck, back away SLOWLY and in a straight line, then lower the pallet down to ground level as soon as it clears the back of the truck. When moving the pallet into the hangar, the pallet will be no more than 6" off the ground.

I do need to be guided since I can't see through the boxes on the pallet. I have to turn 90 degrees and go up a small slope to the entry to the hangar, I drive slowly and cross all slopes at a 90 degree angle, don't let the tractor or the load tilt.

I use the phrases "Moving forward", "Moving back" and "Are you clear?" a lot, and listen for positive confirmation before moving the tractor. I have noticed that people tend to move in for a closer look as work progresses, so I am not shy about chasing them away again to a safe vantage point.

As I mentioned, I have had people walk between the tractor (while it is running) and the truck, and I have had people get within five feet of the tractor when I am making turns (usually standing on the outside of the turn, which is where the boxes will fall if anything goes wrong). I've found that I cannot assume anyone else understands the dangers here, so it is my job to keep them safe, and if they get insulted, that's just too g*****n bad, I'd rather they get insulted than hurt or worse.

People do dumb things all the time, I really, really prefer they do them someplace else.

Best Regards,

Mike/Florida

"Interesting that tilt function doesn't (seem to) be connected with the safety valve (if I read it correctly), which is why I couldn't lift, but I could still tilt."

The lift and tilt spools in the valve are both connected to the same relief valve but only when that spool is being used. The tilt function, in some but not all situations, has more mechanical advantage (but same maximum PSI) than the lift so it is able to raise the load (by tilting) when the lift function may not.

 

[Little Red Tractor]

Assuming that Sunandsand was quoting that magazine article verbatim, that magazine should filter its writers

 

[JWR]

Bentrim said:
"Hydraulics a very simple and confusing topic.
Open Center system. Pump = A positive displacement unit that draws oil from a tank and moves oil to a control device, note a pump does not create pressure it only moves fluid at a set rate per the rpm operated."

The inlet to a pump is at negative pressure causing fluid to enter the pump ("draws" it) from the sump which is at neutral pressure. The outlet of the pump is at a positive pressure which goes to a high number varied by things like relief valves and loads. Obviously the pump DOES create pressure and if it did not the fluid would never move. By definition, and normal specs, a pump creates an amount of flow at a pressure.

What is the point of trying to claim the pump does not create pressure?

 

[Egon]

There are different types of pumps. Positive displacement pump or a centrifugal type pump. They create pressure in different ways.

 

[npalen]

Bentrim said:
"Hydraulics a very simple and confusing topic.
Open Center system. Pump = A positive displacement unit that draws oil from a tank and moves oil to a control device, note a pump does not create pressure it only moves fluid at a set rate per the rpm operated."

The inlet to a pump is at negative pressure causing fluid to enter the pump ("draws" it) from the sump which is at neutral pressure. The outlet of the pump is at a positive pressure which goes to a high number varied by things like relief valves and loads. Obviously the pump DOES create pressure and if it did not the fluid would never move. By definition, and normal specs, a pump creates an amount of flow at a pressure.

What is the point of trying to claim the pump does not create pressure?

I've too have often wondered why folks make that counter intuitive statement. It would be difficult to have pressure without a pump.
I realize that there also has to be resistance of some kind to create pressure.